The present invention generally pertains to a conference calling arrangement for an integrated services digital network and more particularly to improvements for speaker selection and broadcasting for multi-port conference circuitry.
U.S. Pat. No. 4,466,093 teaches a time shared conference arrangement. U.S. Pat. Nos. 4,466,092 and 4,466,094 also teach similar techniques. The assignee of the present application is the successor in all rights, title and interest to the assignee of the U.S. Pat. No. 4,466,093 patent.
This patent teaches the broadcasting of the "loudest speaker" to the other conferees. A series of on-line comparisons is made between the PCM magnitude levels of up to three conferees. Such on-line comparisons require an amount of switching system real time. Next, this patent teaches the comparison of the loudest detected speaker to a threshold level. If the PCM magnitude of the speakers' values exceeds this threshold, then this loudest speaker's PCM sample is broadcast to the other conferees during the appropriate time slots. If the PCM magnitude of the loudest conferee did not exceed the threshold, then the identity of the loudest conferee stored during the previous sampling time period was selected and the corresponding PCM sample broadcast to the other conferees during the appropriate time slots.
This technique provided for rapid switching between the speakers introducing noise. As a result, the overall audible quality broadcast to the conferees is substantially degraded when two or more parties speak simultaneously.
When multiple sound sources are present, the human ear hears a combination of all the various sources. Some of the sources are louder in amplitude than others. The PCM samples, which represent speech sound, of modern digital networks are not directly combinable. Therefore, the human ear listening via a digital switching system does not hear a true combination of each conferee's speech.
PCM data samples are nonlinear logarithmic representations of human speech. Since these PCM samples are nonlinear, they are difficult to combine.
It is an object of the present invention to provide a method for efficiently generating PCM logarithmic values from linear values for rapid retrieval by a PCM speaker control circuit for a time shared conference arrangement of an integrated services digital network (ISDN).